1. Field of the Invention
The invention relates to an intake system of an internal combustion engine, in which a surge tank is provided on the upstream side of individual intake paths that are connected to and communicate with respective cylinders of the engine. The invention also relates to a method of controlling the intake system.
2. Description of Related Art
In a conventional intake system of an internal combustion engine installed on a vehicle, such as an automobile, a surge tank is provided on the upstream side of individual intake paths that are connected to and communicate with respective cylinders of the engine, and an outside-air duct is connected to and communicates with the surge tank, while an air cleaner and a throttle body, for example, are provided in the outside-air duct, as disclosed in, for example, JP-A-H11-117819.
In the internal combustion engine of a type in which injectors are respectively mounted in the individual intake paths, for example, while the engine stops operating, air flows from the outside-air duct into the surge tank with the passage of time, so that the intake passages of the whole intake system are subjected to atmospheric pressure. Furthermore, a slight amount of fuel may drop or leak from injection nozzles of the injectors, and vapors of the fuel may exist in the individual intake paths. In this condition, the concentration of HC in the intake passages that extend from the individual intake paths to the outside-air duct is undesirably increased.
In the above-described situation, if backfire occurs upon start of the engine, the flame in the combustion chambers may propagate to the upstream portion of the intake system, thus causing reduction of the durability of respective components of the intake system.
In view of the above situation, it has been proposed in, for example, JP-U-S59-137368 to inhibit flame propagation to the air cleaner upon occurrence of backfire. In the known example, a normally-open type check valve is provided between the throttle body or a carburetor and the air cleaner in the air duct through which air is introduced into the engine. In operation, the check valve is closed when backfire occurs.
It has also been proposed in, for example, JP-A-2005-188292 to provide an internal combustion engine having a surge tank and a resonator in an intake system, in which flame propagation to the resonator is inhibited even if backfire occurs upon start of the engine. In the known example, an open/close valve is provided in a partition wall that separates the surge tank from the resonator. In operation, the open/close valve is closed when the engine is prepared to be started, and is opened when the engine is started.
It has also been proposed in, for example, JP-A-2003-172237 to provide an internal combustion engine provided with an intake manifold having a specified volume of space in an intake system, and to control the engine so as to suppress or prevent overshoot of the engine speed (i.e., a sudden rise in the rotational speed of the engine) when the engine is started. In the known example, a vacuum tank is connected to and communicates with the specified volume of space in the intake manifold, and an open/close valve (e.g., a solenoid-operated valve) is provided in a communicating portion between the intake manifold and the vacuum tank. In operation, the open/close valve is opened immediately before start of the engine, and is closed when starting of the engine is completed.
In the known example as disclosed in JP-U-S59-137368 identified above, the check valve is closed upon occurrence of backfire so as to inhibit flame propagation to the air cleaner. However, if a surge tank is located upstream of the individual intake paths and downstream of the throttle body as viewed in the direction of flow of the intake air, the flame may propagate into the surge tank.
In the known example as disclosed in JP-A-2005-188292 identified above, the open/close valve is closed upon detection of a request for start of the engine, so that flame propagation to the resonator can be inhibited even if backfire occurs upon start of the engine. With the open/close valve closed, however, the individual intake paths leading to the combustion chambers are held in communication with the surge tank; therefore, the flame may propagate into the surge tank if backfire occurs.
In the known example as disclosed in JP-A-2003-172237 identified above, overshoot of the engine speed at the time of start of the engine can be suppressed or prevented, but occurrence of backfire is not taken into consideration. In this example, when the engine is started, the open/close valve is opened so as to suppress or prevent overshoot of the engine speed, and the intake manifold and the vacuum tank are held in communication with each other. If backfire occurs in this condition, it is difficult or impossible to avoid flame propagation from the intake manifold to the upstream portion of the intake system including the vacuum tank.
Thus, there is some room for improvement in any of the known examples as described above.